This invention relates to an illuminator such as a liquid crystal display device of the so-called back lighting type which does not emit light itself but has a light source behind it such that its visibility can be improved.
An example of such an illuminator was disclosed in Japanese Utility Model Publication Jikko 4-14943 and, as shown in FIGS. 11 and 12, comprises a light-conducting transparent or translucent plate 20' having a uniform thickness and concave indentations 21' near its edges containing light source units 30'. As shown in FIG. 12, the light source unit 30' forms a light-emitting part 33' by placing a LED chip 32' near the bottom of a box-shaped reflector case 31' with an open front, filling the interior of the case with a transparent resin material, and extending a terminal lead line 34' from this light-emitting part 33'. Light emitted from the LED chip 32' is reflected by the inner surfaces of the reflective case 31' and enters the interior of the light-conducting plate 20', spreading throughout the light-conducting plate 20' by repeatedly undergoing total reflections at its top and bottom boundary surfaces and eventually being emitted outward from the surface. As a result, although the light source units 30' are placed at edge portions of the light-conducting plate 20', the entire surface area of the light-conducting plate 20' seems to be shining.
Light emitted from a LED chip is monochromatic. LED chips adapted to emit red, green and blue light are now available. Although white light is ideal for back lighting, green LED chips were usually used as a light source for an illuminator of the type described above if LED chips were to be used as the light source at all. Although a plurality of LED chips are generally placed separate from one another in order to illuminate the entire surface of a light-conducting plate uniformly, since LED chips of the same color are usually used, it was not possible to change the color of emitted light from an illuminator as a whole.